If-Modified-Since header

[Simon Canning]

GET /index.html HTTP/1.1
If-Modified-Since: Sat, 29 Oct 2010 19:43:31 GMT
User-Agent: http protocol
Host: 127.0.0.1
Cache-Control: no-cache

I am sending this header to a server, and the page is still returned even though the modified date is in the future...

Why would this be?

[SambaNeko]

From this page:

A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only if it has been modified since the date given by the If-Modified-Since header. The algorithm for determining this includes the following cases:

a) If the request would normally result in anything other than a
200 (OK) status, or if the passed If-Modified-Since date is
invalid, the response is exactly the same as for a normal GET.
A date which is later than the server's current time is
invalid.

Your date is invalid; the header cannot be used in the way you're trying to use it.

[Simon Canning]

OK, even the following doesnt work:

GET /index.html HTTP/1.1
If-Modified-Since: Mon, 1 Feb 2010 19:43:31 GMT
User-Agent: http protocol
Host: 127.0.0.1
Cache-Control: no-cache

Why would this be?

[SambaNeko]

Could you post some code showing how you're sending this request?

[Simon Canning]

Basically i am using a class module in vb6...

Is that what you are talking about?

[Simon Canning]

Will the If-Modified-Since header only work if the date modified setting is setup on the server?

[SambaNeko]

Is that what you are talking about?

Yes, but I can't help with VB6 anyway.

Will the If-Modified-Since header only work if the date modified setting is setup on the server?

I would assume so.

Are you checking the response code for 304? Even if If-Modified-Since is false, page content could be returned from a cache, but the code should still be 304.

[Simon Canning]

Are you checking the response code for 304

Sorry, im confused... why do i want to do that?

[SambaNeko]

[Assuming the server supports the If-Modified-Since header,] A 304 response is sent back to the requesting client if the page on the server has not been modified; this is the signal for the client to reload the page contents from its cache rather than getting a new copy from the server.

You said "the page still returned" - I'm wondering if you got a 304 response (the result you want), but the page you got was from a cache.

Edit: wait a minute, I just looked at your headers again - if you're not letting the client cache the page (Cache-Control: no-cache), then you're always going to get a new copy of the page from the server. If-Modified-Since is a comparison between the client's cached copy of the page and the server's page. If there's no cached page, no comparison can be made.